This invention relates to surface modification of the slip characteristics of polymeric surfaces. In particular, surfaces of tubing composed of polymeric materials such a silicone rubber, polypropylene, polyethylene, polyvinylchloride, fluoropolymers and the like or other dielectric materials and to improved methods and apparatuses for effecting such modifications.
Polymeric plastic tubing, particularly that of small diameter, and most especially that of silicone rubber, is used in many medical applications and devices. In particular, silicone rubber (especially cross linked silicone elastomer with silica filling) is the polymer of choice for tubing in many medical applications involving implantation.
Catheters prepared from polymeric materials are used frequently in such routine procedures as the delivery of intravenous fluids, removal of urine from compromised patients, chemical sensing using a variety of chemical transducers, monitoring cardiovascular dynamics, and treating cardiac and vascular disorders. Catheters provide the pathway to previously inaccessible body areas for both diagnostic and therapeutic procedures, thereby reducing the need for surgery. For example, double catheter systems are utilized for drug delivery or occlusion of blood flow to specific organs or tissues. Typically, a rigid outer catheter and a buoyant, flexible inner catheter that can freely float in the blood stream are used in such procedures. Another example is a pacing lead which utilizes a small diameter tubing such as less than 0.055 inch (1.40 mm) (OD) with an inner diameter (ID) of 0.35 inch (0.9 mm). In this type of lead, an elongate wire core (usually in the form of a coil) having a helical screw-in electrode at its distal end is placed inside the small diameter tubing to provide a catheter-like device. The core wire is manipulated at the proximal end of this arrangement by the physician during implantation to screw the helical electrode into heart tissue and fix the lead in place. Of course these catheter-like devices may involve other structures not described herein for simplicity.
As catheterization techniques have become more complicated, more demands placed on the performance of the catheter have increased. For instance, the paths that these catheters must take through the body are often long and tortuous, such as accessing the cranial vessels via the femoral artery. The polymeric materials from which catheters are made, such as silicone rubber, have a tacky surface upon exposure to an aqueous environment. This causes excessive friction, making placement of the catheter-like device in the body difficult. Further, these friction characteristics also make torque transfer through the tubing difficult thus, for example, making difficult the turning of the core wire which is preferably a torsion coil in the aforementioned "screw in" pacing lead to screw the helical electrode into tissue.
Previous practices to ameliorate these friction characteristics have involved: 1) the use of harder materials which are more slippery but less biostable and less suitable for implantation, e.g., polyurethane; 2) coating; 3) hardening; 4) swelling; and even 5) the use of environmentally unfriendly materials such as chlorofluorocarbons (CFC). For example, polyurethane catheters have been coated with a composition of a poly(vinyl pyrrolidone) (PVP) crosslinked with an isocyanate (commercially available under the trade designation "HYDROMER" from Hydromer Inc., New Jersey). See, eg., "Reduced Frictional Resistance of Polyurethane Catheter by Means of a Surface Coating Procedure," by Nurdin, N., et al., Journal of Applied Polymer Science, Vol. 61, 1939-1948 (1996), herein incorporated by reference.
Plasma discharge has also been used on tubing with some degree of success. More specifically, exposure of polymeric surfaces to plasma discharge is effective in modifying the surface to improve its slip characteristics. For example, U.S. Pat. No. 5,593,550 (Stewart et al.) is directed to a plasma process for improving the slip characteristics of polymeric tubing on its OD and ID. U.S. Pat. No. 5,133,422 (Coury et al.) is directed to improving the slip characteristics of polymeric tubing on its OD by plasma treatment in the presence of a gas selected from the group consisting of hydrogen, nitrogen, ammonia, oxygen, carbon dioxide, C.sub.2 F.sub.6, C.sub.2 F.sub.4, C.sub.3 F.sub.6, C.sub.2 H.sub.4 C.sub.2 H.sub.2, CH.sub.4, and mixtures thereof. U.S. Pat. No. 4,692,347 (Yasuda) is directed to plasma deposition of coatings and to improving blood compatibility on both the OD and the ID surfaces of polymeric tubing by coating it under discharge conditions in a single chamber.
The theory and practice of radio frequency (RF) gas discharge is explained in detail in 1) "Gas-Discharge Techniques For Biomaterial Modifications" by Gombatz and Hoffman, CRC Critical Reviews in Biocompatibility, Vol. 4, Issue 1 (1987) pp 1-42; 2) "Surface Modification and Evaluation of Some Commonly Used Catheter Materials I Surface Properties" by Triolo and Andrade, Journal of Biomedical Materials Research, Vol. 17, 129-147 (1983), and 3) "Surface Modification and Evaluation of Some Commonly Used Catheter Materials, II. Friction Characterized" also by Triolo and Andrade, Joumal of Biomedical Materials Research, Vol. 17, 149-165 (1983). All of the foregoing are incorporated herein by reference.
A number of patents have been reviewed in which plasma reactors are disclosed which use wave energy (RF or microwave) to excite plasma. Although not admitted as prior art, examples of plasma reactors and methods using the same can be found in the issued U.S. Patents listed in Table 1 below.
______________________________________ LIST OF U.S. PATS. ______________________________________ U.S. PAT. NO. 5,593,550 01/14/1997 Stewart et al. U.S. PAT. NO. 5,244,654 09/14/1993 Narayanan U.S. PAT. NO. 5,223,308 06/29/1993 Doehler U.S. PAT. NO. 5,133,986 07/28/1992 Blum et al. U.S. PAT. NO. 5,133,422 07/28/1992 Coury et al. U.S. PAT. NO. 4,948,628 08/14/1990 Montgomery et al. U.S. PAT. NO. 4,927,676 05/22/1990 Williams et al. U.S. PAT. NO. 4,846,101 07/11/1989 Montgomery et al. U.S. PAT. NO. 4,752,426 06/21/1988 Cho U.S. PAT. NO. 4,718,907 01/12/1988 Karwoski et al. U.S. PAT. NO. 4,692,347 09/08/1987 Yasuda U.S. PAT. NO. 4,448,954 12/18/1984 Hatada et al. U.S. PAT. NO. 4,261,806 04/14/1981 Asai et al. ______________________________________
It is a primary object of this invention to provide polymeric surfaces which exhibits improved slip characteristics. This and other objects will be clear from the following description.